Fluid triode



July 15, l969 s. E. LIGHTNER.'

FLUID TRIODE Filed April 29,- 196e Hua GENE E. LIGHTNER @20M/MQW ATTORNEY United States Patent O 3,455,326 FLUID TRIODE Gene E. Lightner, St. Louis, Mo., assignor to Monsanto Company, St. Louis, Mo., a corporation of Delaware Filed Apr. 29, 1966, Ser. No. 546,235 Int. Cl. Fc 1/02; F16k 9/ 00; F161 43/00 U.S. Cl. 137-253 10 Claims ABSTRACT OF THE DISCLOSURE A fluid triode operable as an analog of an electrical triode and comprising a substantially U-shaped housing with a pair of upstanding legs which are connected by a bight portion. A secondary fluid is located in the houslng and extends into each of the two legs and across the bight portion. A control pressure inlet is formed in one of the legs and communicates with the secondary fluid in the housing by raising and lowering the level of the secondary fluid responsive to changes in the control pressure. A primary fluid inlet is formed in one of said legs opposite that having the control pressure inlet and introduces a primary fluid in the housing responsive to a supply lpressure. A gate forming plug covers the open end of the primary fluid inlet. Thus, changes in the control pressure will change the height of the secondary fluid thereby changing the head against which primary fluid flows for modulation of the flow of primary fluid to thereby control the amplification of the supply pressure signals. The gate forming plug is substantially pervious to the passage of the primary fluid and substantially impervious to the passage of the secondary fluid.

This invention relates in general to certain new and useful improvements in fluid control devices, and more particularly to fluid triodes which are caable of converting either pressure or mechanical motion to a pneumatic pressure or flow signal.

Fluid amplifiers which have no moving parts except for the fluid itself have been finding widespread use in a wide variety of applications where electronic components have previously been employed. There are a number of commercially available types of fluid amplifiers such as the stream interaction or momentum interchange type, where a power nozzle is supplied with pressurized fluid and issues a power jet or stream. A control nozzle directs the fluid against the side of the power jet and dellects the power jet away from the control nozzle. In this manner, it is possible to direct a high powered jet toward or away from a target area in response to a control stream of substantially lower power.

Another type of fluid amplifier commonly employed is the so-called boundary layer fluid amplifier where a high energy jower jet is directed toward a target area by pressure distribution in a power jet boundary layer region. The pressure distribution is controlled by wall configuration. The device is designed so that the jet will lock onto one side wall in the boundary layer region and remain in the locked-on configuration even without control fluid flow.

Each of the amplifiers heretofore provided required a moving control stream. In other words, the control stream itself had to exert some moving force on the power stream in order to obtain amplification characteristics. Because of the nature of this type of device, it has been almost impossible to scientifically design fluid amplifiers. The interactions of the fluid circuit elements where two or morev streams of moving fluids are combined makes fluid circuit design extremely diflicult. Accordingly, the amice plifiers heretofore provided were mainly fabricated by so-called cut and try methods.

In the past, the accurate design of fluid control components such as fluid diodes, etc. presented a large problem to fabrication of such components. The hydrodynamics of the fluid amplification devices are dependent on flow rates through the devices and the geometry of the devices. The mathematics of the design equations are complex and three dimensional equations were often employed to determine design. Slight changes in the specification of design often deviated from the basic set of stipulations and accordingly, the fabricator `was compelled to design on a trial and error basis.

. It is, therefore, the primary object of the present invention to provide a fluid triode which is capable of being operated without interactions of fluid circuit elements.

It is another object of the present invention to provide a fluid triode of the type stated where the input impedance is ractive and is essentially infinite at steady state.

It is a further object of the present invention to provide fluid triodes of the type stated where a field is established by the control pressure acting on a column of liquid.

It is also an object of the present invention to provide a fluid triode of the type stated which has no moving mechanical parts and employs a fluid media as a variable fluid resistance.

It is another salient object of the present invention to provide a Ifluid triode of the type stated which is useful in a wide variety of applications and can be constructed at a relatively low unit cost.

With the above and other objects in View, my invention resides in the novel features of form, construction, arrangement and combination of parts presently described and pointed out in the claims.

In the accompanying drawings (l sheet):

FIGURE 1 is a schematic side elevational View of a fluid triode constructed in accordance with and embodying the present invention; and

FIGURE 2 is a graphical illustration of the flow characteristics of the fluid triode showing the differential pressure across the triode as a function of air flow.

General description Generally speaking, the fluid triode of the present invention comprises an outer housing which is generally U-shaped and is formed with a single chamber containing a control pressure fluid. The housing is provided with a control pressure inlet and a primary outlet. The control pressure inlet acts upon a secondary fluid contained in one leg of the U-shaped housing, which in turn affects the level of the secondary fluid in the opposite leg of the housing. The opposite leg of the housing is also provided with a primary fluid inlet, somewhat below the level of the secondary fluid. The primary fluid preferably in the form of a gas is then bubbled through the secondary fluid, thereby providing modulation by the column height of the secondary fluid. Consequently, the fluid triode is analogous to an electrical triode.

Detailed description Referring now in ymore detail and by reference characters to the drawings which illustrate a preferred embodiment of the present invention, A designates a fluid triode generally comprising an outer housing 1, which is preferably formed of any suitable metal, such as aluminum or stainless steel or any available plastic or synthetic resin material. The housing 1 s generally of U-shaped configuration including a pair of legs 2, 3 connected by a bight portion 4 for containing a secondary fluid hereinafter 4described in more detail. The leg 3 is of a substantially larger diameter than the leg 2. The

leg 3 integrally merges at its upper end into a discharge tube 5, which is horizontally disposed and located approximately at right angles to the leg 3. The leg 2 is provided with a control pressure inlet port 6 and the discharge tube is provided with an outlet port 7.

The leg 3 is suitably apertured somewhere near the lower end for .accommodating a horizontally disposed supply pressure tube 8 which is curved upwardly in the interior of the leg 3 by a neck 9 and terminates in a a vertical stem 10, which provides a primary inlet for introducing a primary uid. A porous plug 1l, which serves as a gate, is inserted in the upper end of the stem portion 10, in the manner as illustrated in FIG- URE 1. The plug 11 is preferably formed of sintered stainless steel of approximately 0.5 to 2.0 microns diameter pores. Ceramics such as silica, alumina, chromium, or other ceramic materials, etc. may also be effectively employed as a gate-forming plug 11. Moreover, polymers such as sintered Teflon and polyolefins, vinyls, etc., and copolymers such as nylon, etc. may also be employed as the plug 11.

The secondary uid which is contained in the housing 1 generally has a normal level when no control pressure is applied above the porous plug 11 that is the same level would exist in eacs of legs 2 and 3. A very suitable secondary uid is mercury or any other fluid which is immiscible with the primary fluid and will serve as a variable fluid resistance.

The primary fluid will serve as a control or -bias pressure and is preferably a gas such as air, nitrogen, or any other uid which is immiscible with and has a lower density than the secondary fluid. A control pressure source is applied to the inlet port 6, thereby maintaining a bias on the level in the legs 2 and 3.

Other primary iluids which may be employed in the present invention are gases or vapors or liquids which are immiscible and non-reactive with the secondary fluids; such uids are water, air steam, oxygen, hydrogen, nitrogen, argon, neon, helium, etc. Suitable secondary fluids which may be employed in the practice of the present invention are dependent upon the interfacial tension with the gate-forming material since breakdown pressure is affected by interfacial tension and pore diameter. Such materials are water, mercury, liquid hydrocarbon, silicon uids, etc. However, the secondary fluid should have a high surface tension. A few suitable combinations are set forth below. However, the present invention is in no way limited to this list of usable materials.

Secondary luid Primary fluid Gate-forming material sintered stainless steel.

tion.

It is, of course, obvious that care must be taken when selecting these combinations. For example, a primary fluid could not be reactive with a secondary fluid. Furthermore, highly reactive materials such as chlorine are not particularly suitable.

The fluid supplied to the present iiuid triode in general can be of any type. The utilization of the term fluid encompasses any gas, liquid, semi-solid or similar type of material 'which can be caused to flow under the application of a pressure differential. It should also be understood that the term lluid refers to any mixture or combination of materials that can be individually used, such as water intermixed with a stream of air.

It can 'be seen that the level of secondary fluid in the leg 3 forms a head of pressure against which the primary uid or supply pressure must overcome before the uid triode A will operate in the active region. The active region may be dened as the region where llow occurs CII at bias pressures of zero and all bias pressures below zero. The plug 11 serves as a gate-forming material. Where the level of mercury in the leg 3 is high, the supply pressure will have to overcome a substantially great pressure head and only a small quantity of air will pass through the secondary iluid per unit of time. Similarly when the control pressure is substantially reduced, the level of the secondary liuid in the leg 3 forms a head of pressure against which the primary fluid or supply pressure must overcome before the fluid triode A will operate. Consequently, more primary uid will flow through the secondary fluid and through the output air flow.

The characteristics in the operation of the fluid triode A are analogous to a vacuum tube triode. Simple comparison of this fluid triode with a vacuum tube triode will illustrate the close resemblance of these two distinct devices. Furthermore, it should `be recognized that the fluid triode of the present invention may be used in any uid circuit Where its analogue, the vacuum triode may be used in any electrical circuit.

It can thus be seen that the uid triode A operates as an isolation device Where isolation may be defined as the amplification of a pressure signal from a high impedance source by means of an isolated control signal. In essence, the control signal source is not loaded down. Accordingly, the ow is created from the signal so that, in effect, an isolated signal is provided. By means of this construction, it is possible to provide amplication without distortion to the control signal. In this manner, the liuid triode A is substantially similar to the electrical analogue of the triode.

The vacuum tube triode is in general a non-linear circuit device and the operation of the vacuum tube triode is predictable by a functional relation of the current, the plate current, and grid voltage and control voltage. Thus, such two variable curves can be constructed by holding one of the variables constant in each case. Similarly, constant current family and plate voltage-plate current curves may also be drawn for the vacuum tube triode. Similar curves can also be drawn for the uid triode, which are very similar to the families of curves obtained for an ideal linear vacuum tube triode.

The basic equations which describe the fluid triode are set forth below. The control pressure is related to the output pressure, the ilow rate and the resistance across the porous plug by the equation where:

Pc is the control pressure Po is the ouptut pressure Q is the flow rate, and

Rp is the resistance across the porous plug.

The ratio of the incremental change in output pressure to the incremental change in input pressure is given by differentiating Equation 3 6P R 6P, n+1-2 (4) This latter equation defines the gain of the amplifier.

The fluid triode s unique in that it is capable of converting either pressure or mechanical motion to a pneumatic pressure or a liow signal. The uid triode A has a long life inasmuch as only two mmiscible fluids are involved and no moving parts are employed. Simple mechanical motion of one leg 2 of the housing 1 may be transmitted directly into the pressure signal. This could be accomplished if the bight portion 4 were formed of a flexible material. Furthermore, interactions of fluid circuit elements can be avoided by the use of low impedance fluid pressure supplies. From the above, it can be seen that the fluid triode A can be used as a process control element such as a transducer, a relay or a controller. In the electronic triode, the control field simply raises or lowers the potential barrier for electron flow. That is, current flow is determined by the number of electrons which have kinetic energy equal to or greater than the potential barrier of the field. In the fluid triode, however, the field is established by the control pressure acting on a column of liquid. The supply air flow bubbling through the liquid is modulated by the column height. Accordingly, it is again seen that the fluid triode can not only be used in the applications where its anaolgue, the electrical triode, can be used in electrical circuits, but can be used in a multitude of applications.

The invention is further illustrated by, but not limited to the following example.

Example A fluid triode is constructed of a clear Lucite plastic material having an overall thickness of approximately 11/2. The housing was U-shaped with the smaller diameter leg having an inner diameter of approximately 1/2" and the larger leg having an inner diameter of approximately l". The primary or supply pressure inlet tube had an inner diameter of approximately 1/2. The air input was connected direclty to the pressure supply and an air pressure source was also connected to the secondary inlet or control pressure. The supply pressure and the control pressure are adjusted by Mason-Eiland pressure regulators which are interposed within each of the fluid lines. Mercury is employed as the secondary fluid and air is employed as the primary fluid. Fluctuations in the gate pressure or control pressure causes the mercury level to rise or fall so as to increase or decrease the head of secondary fluid against which the air pressure source must overcome to provide modulation of the secondary fluid flow of the triode.

Characteristic curves were obtained by the test circuit indicated above and the fluid triode characteristics were thus determined. These curves are illustrated in FIGURE 2. The change in pressure, that is the pressure from the porous plug to the outlet was plotted as a function of the flow in cubic feet per minute. This plot was made for various bias or control pressure levels, which was the operating parameter. It is found that completely linear response is obtained. It again should be recognized that there is a maximum critical limit at which the triode will become unstable due to the channelling of gas flow. This imposes a maximum limit on the allowable pressure drop across the fluid amplifier. However, the amplifier provides excellent linearity in the desired range of operation.

It should be understood that changes and modifications in the form, construction, arrangement and combination of parts presently described and pointed out may be made and substituted for those herein shown without departing from the nature and principle of my invention.

Having thus described my invention, what I desire to claim and secure by Letters Patent is:

1. A fluid control element comprising:

(a) ahousing,

(b) a secondary fluid in said housing,

(c) a fluid outlet in said housing above the level of the secondary fluid,

(d) a control pressure inlet communicating with the secondary fluid in said housing and raising and lowering the level of secondary fluid in said housing by changes in isolated control pressure signals,

(e) a primary fluid inlet in said housing opening into said secondary fluid and introducing a primary fluid from a high impedance source in said housing responsive to a supply pressure signal for amplification of said supply pressure signal Iby means of said isolation control pressure signals, said primary fluid inletl having an opening below said secondary fluid eve (f) and a constant flow area gate-forming plug covering the entire open end of said primary fluid inlet and being substantially pervious to the passage of said primary fluid and substantially impervious to the passage of said secondary fluid,

whereby changes in control pressure will change the height of secondary fluid in said housing, thereby modulating the flow of the primary fluid to control the amplification of said supply pressure signals.

2. The fluid control element of claim 1 wherein the primary and secondary fluids are immiscible.

3. The fluid control element of claim 1 wherein the primary fluid is ta gas and the secondary fluid is a liquid.

4. The fluid Vcontrol element of claim 1 wherein the primary fluid is air, the secondary fluid is mercury and the gate-forming plug is a porous sintered stainless steel.

5. The fluid control element of claim 2, wherein said element functions as a transducer for converting motion to pressure signals.

6. The fluid control element of claim 2, wherein said element functions las a transducer for converting motion to fluid flow signals.

7. The fluid control element of claim 1 wherein the housing is U-shaped.

8. The fluid control element of claim 1 wherein the housing is U-shaped formed by a pair of legs and one of the legs has a larger internal diameter than the other of said legs.

9. A fluid control element comprising:

(a) a U-shaped outer housing having a first leg with a -small diameter interior bore and a second leg with a large diameter interior bore,

(b) a bight portion connecting each of said legs,

(c) a secondary fluid in said housing,

(d) a fluid outlet in the second leg of said housing above the level of the secondary fluid,

(e) a control pressure inlet in said first leg communicating with the secondary fluid in said housing and raising and lowering the level of secondary fluid in said second leg of said housing Iby changes in isolated control pressure signals introduced in said first leg,

(f) a primary fluid inlet into the second leg of said housing and opening into said secondary fluid for introducing a primary fluid from a high impedance source in the second leg of said housing responsive to a supply pressure signal for amplification of said supply pressure signals by means of said isolation control pressure signals, said primaryfluid inlet having an internal bore diametrally smaller than said second leg and having an opening below the secondary fluid level in said second leg,

(g) and a constant flow area gate-forming plug covering the entire open end of said primary fluid inlet and being substantially pervious to the passage of said primary fluid and substantially impervious to the passage of said secondary fluid,

whereby changes in control pressure will change the height of secondary fluid in said housing, thereby modulating the flow of the primary fluid to control the amplification of said supply pressure signals.

10. A fluid triode having a reactive input impedance which is essentially infinite at steady state conditions, said trode comprsing:

(a) ahousing,

(b) a secondary fluid in said housing,

(c) a fluid outlet in said housing :above the level of the secondary fluid,

(d) a control pressure inlet communicating with the secondary Huid in said housing and raising and lowering the level of secondary iluid in said housing by changes in isolated control pressure signals,

(e) a primary fluid inlet in said housing opening into said secondary uid and introducing a primary fluid from a high impedance source in said housing responsive to a supply pressure signal for amplification of said supply pressure signals by means of said isolation control pressure signals, said primary uid inlet having an opening below said secondary uid level,

(f) and a constant ow area gate-forming plug covering the entire open end of said primary fluid inlet and being substantially pervious to the passage of said primary fluid and substantially impervious to the passage of said secondary iluid,

whereby changes in control pressure will change the height of secondary fluid in said housing, thereby modulating the How of the primary uid to control the amplification of said supply pressure signals.

References Cited FOREIGN PATENTS 7/1960 Great Britain.

WILLIAM P. ODEA, Primary Examiner o DENNIS H. LAMBERT, Assistant Examiner U.S. Cl. XR. 

